Bài giảng Công nghệ Java: Chương 13 - PhD. Trần Quang Diệu

• A collection is an object that groups multiple elements into a single unit.. • Very useful.[r]

4/7/2018 http://sites.google.com/site/tranlectures 1

CÔNG NGHỆ JAVA

CH13 JAVA COLLECTIONS

Quang Dieu Tran PhD.

http://sites.google.com/site/tranlectures

Readings and References

• References

– "Collections", Java tutorial

Java 2 Collections

• A collection is an object that groups multiple

elements into a single unit

• Very useful

– store, retrieve and manipulate data

– data structures and methods written by hotshots in the field

• Joshua Bloch, who also wrote the Collections tutorial

Collections Framework

• Unified architecture for representing and

manipulating collections

• A collections framework contains three things

– Interfaces

Collections Framework Diagram

•Interfaces, Implementations, and Algorithms

•From Thinking in Java, page 462

Collection Interface

• Defines fundamental methods

– int size();

– boolean isEmpty();

– boolean contains(Object element);

– boolean add(Object element); // Optional

– boolean remove(Object element); // Optional

– Iterator iterator();

• These methods are enough to define the basic

behavior of a collection

• Provides an Iterator to step through the elements in the Collection

Iterator Interface

• Defines three fundamental methods

– Object next()

– boolean hasNext()

– void remove()

• These three methods provide access to the

contents of the collection

• An Iterator knows position within collection

• Each call to next() “reads” an element from the

collection

– Then you can use it or remove it

Iterator Position

Example - SimpleCollection

public class SimpleCollection {

public static void main(String[] args) {

Collection c;

c = new ArrayList();

System.out.println(c.getClass().getName());

for (int i=1; i <= 10; i++) {

c.add(i + " * " + i + " = "+i*i);

} Iterator iter = c.iterator();

while (iter.hasNext())

System.out.println(iter.next());

}

}

List Interface Context

Collection

List